The present invention relates generally to cyclonic separators. In one particular application, the invention relates to the cyclonic separation of particulate material from an air flow. In a preferred embodiment, the cyclonic separator is used in a vacuum cleaner to remove entrained particulate matter from an air stream.
The use of a cyclone, or multiple cyclones connected in parallel or series, has long been known to be advantageous in the separation of particulate matter from a fluid stream. Typically, a relatively high speed fluid stream is introduced tangentially to a generally cylindrical or frusto-conical container, wherein the dirty air stream is accelerated around the inner periphery of the container. The centrifugal acceleration caused by the travel of the fluid in a cyclonic stream through the cyclone causes the particulate matter to be disentrained from the fluid flow and, eg., to collect at the bottom of the container. A fluid outlet is provided for the extraction of the fluid from the centre of the top of the cyclone container, as is well known in the art.
A typical flow path in a cyclone separator is as follows. Fluid to be treated is introduced tangentially at a fluid inlet located at an upper end of the cyclone container. The fluid stream rotates around the inner surface of the cyclone container, and spirals generally downwardly around the inner surface of the container (if the cyclone container is vertically disposed). At a bottom end of the cyclone container the fluid stream travels radially inwardly, generally along the bottom of the container and then turns upwardly and proceeds vertically up and out of the cyclone container. The particulate matter separating action of the cyclonic flow occurs substantially around the inner surface of the container. Once the fluid moves inwardly to the centre of the container, and upwardly there through, there is little or no dirt separation achieved.
The difficulty experienced with prior art cyclonic separators is the reentrainment of the deposited particles back into the outgoing fluid flow. Deposited particles exposed to a high speed cyclonic flow thereover have a tendency to be reentrained. This is particularly problematic when the container has a solid bottom portion in which the dirt collects. However, there is a potential reentrainment problem even if the bottom of the container has a passageway provided in the bottom thereof to convey the separated particulate material away from the container.
If a high degree of separation is required, it is known to connect a plurality of cyclones in series. While using several cyclones in series can provide the required separation efficiency, it has several problems. First, if the separators are to be used in industry, they generally need to accommodate a high flow rate (eg. if they are to be used to treat flue gas). The use of a plurality of cyclones increases the capital cost and the time required to manufacture and install the separators. Further, the use of a plurality of cyclones increases the space requirements to house the cyclones as well as the back pressure caused by the air flow through the cyclones. These latter issues are particularly acute for cyclone separators which are to be contained in a small housing, such as a vacuum cleaner. Accordingly, there is a need for an improved anti-reentrainment means for cyclonic separators.
In has now been discovered that a single cyclone having improved efficiency (eg. up to 99.9% efficiency) may be manufactured by positioning in the cyclone chamber a particle separation member for creating a dead air space beneath the cyclonic flow region of the cyclone chamber wherein the dead air space is in communication with the cyclonic flow region by a plurality of openings or apertures in the member. This construction effectively traps separated material beneath the cyclonic flow region and inhibits the reentrainment of the separated material. Thus, a single cyclone may be used in place of a plurality of cyclones to achieve the same separation efficiency.
As the fluid flow travels through the cyclone chamber, a boundary layer forms. Generally, the interior surface of a cyclonic chamber is smooth so as to provide for an uninterrupted cyclonic flow in the chamber. However, in the chamber, a boundary layer is still formed on all surfaces over which the fluid passes. According to the instant invention, the system (i.e. the motor means to move the fluid through the chamber, the fluid inlet to the chamber, the fluid outlet to the chamber and/or the construction of the separation member) is designed to minimize the thickness of the boundary layer in the vicinity of the apertures in the separation member.
In particular, as the fluid travels over the upper surface of the particle separation member, a boundary flow layer will form. The boundary layer will thicken until a thickness is reached at which the boundary layer has sufficient energy to break off and travel away from the upper surface. Generally at this point, the fluid travels upwardly to the fluid outlet from the cyclone. When the boundary layer breaks off from the upper surface, vortices are formed in the fluid stream adjacent the apertures in the separation member causing localized turbulence. The turbulent flow reentrains particles that had been separated from the fluid flow and may even pull some of the separated particles out of the dead air space beneath the cyclonic flow region of the cyclone chamber.
In one embodiment of the instant invention, the cyclonic separator is constructed to minimize the thickness of the boundary layer when it breaks off thereby reducing turbulent flow in the vicinity of the apertures. This may be achieved by varying one or more of the number of apertures in the particle separation member, the length of the apertures, the width of the apertures, the included angle between the upstream edge of the apertures and the upper surface of the particle separation member, the included angle between the downstream edge of the apertures and the upper surface of the particle separation member, and the position of a baffle beneath the particle separation member with respect to the point at which the cyclonic air flow changes direction at the bottom of the cyclone chamber. The actual design of the system will changes in the size of the cyclone chamber, the velocity of the fluid flow in the cyclone chamber and the viscosity of the fluid flow in the cyclone chamber.
In another embodiment, the flow of the fluid itself may be modified to minimize the thickness of the boundary layer when it breaks off. For example, the fluid flow may be pulsed with the frequency of the pulses set to reduce the maximum thickness of the boundary layer. By pulsing the fluid flow, the fluid flow is cyclically accelerated and decelerated. This cyclicling is set to encourage the boundary layer to break off when it is thinner than when the fluid flow is not pulsed. The acceleration after the deceleration provides sufficient energy to cause the boundary layer to delaminate sooner than it would in a constant flow regime thereby reducing turbulent flow in the vicinity of the apertures. This pulsed flow may be achieved in several ways such as by sending a pulsed electrical signal to the fluid pump which produces the fluid flow through the cyclone chamber, by pulsing the fluid as it passes through the cyclone air inlet (eg. the inlet may have an aperture that may be cyclically opened and closed at produce the pulsed flow), by pulsing the fluid as it passes through the cyclone air outlet (eg. the outlet may have an aperture that may be cyclically opened and closed at produce the pulsed flow), or by rotating the particle separation member in its plane (eg. by mounting the particle separation member with a spring biasing means so that the particle separation member will cyclically rotate clockwise and then counter clockwise).
The prior art teaches the need for a plurality of cyclones in order achieve ultra-high particle separation efficiencies. However, it has been found that ultra-high efficiencies can be obtained in a single stage cyclone incorporating the particle separation member of the present invention. Accordingly, cleaning efficiencies in excess of 99% may be obtained with a single stage separator utilizing a separator according to the present invention, thereby negating the need for second stage cyclonic separation altogether. Cleaning efficiencies of over 99.5% have also been achieved for particle laden air streams.
In accordance with the instant invention, there is provided a separator for separating entrained particles from a fluid flow, the separator comprising a separator for separating entrained particles from a fluid flow, the separator comprising:
(a) a cyclone chamber having an outer wall and a cyclonic flow region;
(b) a fluid inlet for introducing a cyclonic fluid flow to the cyclonic flow region;
(c) a fluid outlet for removing the fluid flow from the cyclone chamber;
(d) a particle separation member positioned in the cyclone chamber beneath at least a portion of the cyclonic flow region, the particle separation member having an upper surface and plurality of apertures; and,
(e) a particle receiving chamber disposed beneath the particle separation member for receiving particles passing into the particle receiving chamber through the apertures
wherein the separator is constructed to reduce turbulent fluid flow in the vicinity of the apertures.
In accordance with the instant invention, there is also provided a separator for separating entrained particles from a fluid flow, the separator comprising:
(a) a cyclone chamber for containing a cyclonic flow in a cyclonic flow region;
(b) fluid entry means for introducing a fluid flow to the cyclone flow region for cyclonic rotation therein;
(c) fluid exit means for removing the fluid flow from the cyclone chamber;
(d) fluid pump means for causing fluid flow through the cyclone chamber;
(e) particle receiving means disposed beneath the cyclone flow region for receiving particles separated from the fluid flow;
(f) separation means for dividing the particle receiving means from the cyclone chamber;
(g) transporting means associated with the separation means for connecting the particle receiving means in flow communication with the cyclonic flow region such that, in operation, a boundary layer flow of fluid develops over the separation means and the particles disentrained from the fluid flow pass through the transporting means to the particle receiving means; and,
(h) means for reducing the thickness of the boundary layer of fluid as it travels over the separation means.
In one embodiment, the means for reducing the thickness of the boundary layer comprises means for pulsing the fluid flow through the cyclone chamber. The means for pulsing the fluid flow through the cyclone chamber may comprise means for pulsing an electrical signal to the fluid pump means. Alternately, or in addition, the means for pulsing the fluid flow through the cyclone chamber may comprise means pulsing for cyclically opening and closing one of the fluid entry means and the fluid exit means.
In another embodiment, the means for reducing the thickness of the boundary layer comprises constructing and positioning the transporting means to reduce turbulent fluid flow over the separation means.
In another embodiment, the means for reducing the thickness of the boundary layer comprises constructing and positioning flow disruption means beneath the separating means for disrupting cyclonic fluid flow in the particle receiving means.
In another embodiment, the particle receiving means comprises a sealed chamber except for the transporting means and the separator further comprises emptying means for emptying the particle receiving means.
In accordance with the instant invention, there is also provided a method for separating entrained particles from a fluid flow, the method comprising the steps of:
(a) introducing a fluid to flow cyclonically in a chamber having a cyclonic flow region and a particle separation member positioned in the cyclone chamber to define a particle receiving chamber;
(b) adjusting the back pressure in the chamber to promote the formation of a laminar boundary layer adjacent the particle separation member;
(c) removing particles from the fluid flow in the cyclone chamber via passages provided in the particle separation member; and,
(d) removing the fluid flow from the chamber.
In one embodiment, the method further comprises the steps of storing the particles removed from the fluid flow and inverting the chamber to remove the separated particles.
In another embodiment, the particle separation member is constructed and positioned to reduce turbulent fluid flow over the particle separation member in the vicinity of the passages and the method further comprises passing the fluid flow over the particle separation member during operation of the chamber.
In another embodiment, the chamber further comprises further comprising flow disruption means which is constructed and positioned beneath the separating means for disrupting cyclonic fluid flow in the particle receiving chamber to reduce turbulent fluid flow over the particle separation member in the vicinity of the passages and the method further comprises passing the fluid flow over the particle separation member during operation of the chamber.
In accordance with the instant invention, there is also provided a vacuum cleaner comprising:
(a) a cyclone chamber having an outer wall and a cyclonic flow region;
(b) a fluid inlet for introducing a cyclonic fluid flow to the cyclonic flow region;
(c) a cleaner head adapted for movement over a surface and having a fluid nozzle positionable adjacent the surface, the nozzle in fluid flow communication via a passageway with the fluid inlet;
(d) a fluid outlet for removing the fluid flow from the cyclone chamber;
(e) a particle separation member positioned in the cyclone chamber beneath at least a portion of the cyclonic flow region, the particle separation member having an upper surface and plurality of apertures; and,
(f) a particle receiving chamber disposed beneath the particle separation member for receiving particles passing into the particle receiving chamber through the apertures,
wherein the separator is constructed to reduce turbulent fluid flow in the vicinity of the apertures.
In accordance with the instant invention, there is also provided a vacuum cleaner comprising:
(a) a cyclone chamber having an outer wall and a cyclonic flow region;
(b) a air inlet for introducing a cyclonic air flow to the cyclonic flow region;
(c) a cleaner head adapted for movement over a surface and having a air nozzle positionable adjacent the surface, the nozzle in air flow communication via a passageway with the air inlet;
(d) a air outlet for removing the air flow from the cyclone chamber;
(e) a particle separation member positioned in the cyclone chamber beneath at least a portion of the cyclonic flow region, the particle separation member having an upper surface and plurality of apertures;
(f) a particle receiving chamber disposed beneath the particle separation member for receiving particles passing into the particle receiving chamber through the apertures; and,
(g) a motor for causing the air to flow through the vacuum cleaner
wherein the air flow through the cyclone chamber is pulsed.
In one embodiment, the vacuum cleaner further comprises a moveable closure member on one of the air inlet and the air outlet for causing a pulsed air flow through the cyclone chamber.
In another embodiment, the motor receives an electrical signal and the electrical signal is pulsed to produce the pulsed air flow.
In accordance with the instant invention, there is also provided a vacuum cleaner comprising:
(a) a cyclone chamber having an outer wall and a cyclonic flow region;
(b) a air inlet for introducing a cyclonic air flow to the cyclonic flow region;
(c) a cleaner head adapted for movement over a surface and having a air nozzle positionable adjacent the surface, the nozzle in air flow communication via a passageway with the air inlet;
(d) a air outlet for removing the air flow from the cyclone chamber;
(e) a particle separation member positioned in the cyclone chamber beneath at least a portion of the cyclonic flow region, the particle separation member having an upper surface and plurality of apertures;
(f) a particle receiving chamber disposed beneath the particle separation member for receiving particles passing into the particle receiving chamber through the apertures; and,
(g) a handle for moving the cleaner head over the floor; and,
(h) a motor for causing the air to flow through the vacuum cleaner
wherein the particle separation member is constructed and adapted to increase the particle separation efficiency of the cyclone chamber.
In one embodiment, the particle separation member has from 5 to 35 apertures.
In another embodiment, the number of apertures in the particle separation member is calculated by the formula:       number    ⁢          xe2x80x83        ⁢    of    ⁢          xe2x80x83        ⁢    apertures    =                    H        D            xc3x97      4        ±          20      ⁢      %      
where H=the vertical height of the cyclonic flow region
D=the diameter of the cyclone chamber
In another embodiment, the cyclone chamber has a diameter and each aperture has a longitudinally extending upstream edge and a longitudinally extending downstream edges, relative to the air flow, and transverse sides extending between the edges, the edges have a length which is less than 10% of the diameter of the cyclone chamber and the sides have a length which is 25-35% of the length of the edges.
In another embodiment, the edges are substantially radially aligned with the cyclone chamber.
In another embodiment, each aperture has an upstream edge and a downstream edge, relative to the air flow, and the upstream edge is angled towards the particle receiving chamber, the included angle between the upstream edge and the upper surface of the particle separation member is from 15 to 90xc2x0.
In another embodiment, each aperture has an upstream edge and a downstream edge, relative to the air flow, and the downstream edge is angled towards the particle receiving chamber, the included angle between the downstream edge and the upper surface of the particle separation member is from 15 to 90xc2x0.
In another embodiment, the air flow changes direction and travels to the air outlet at a position as it travels over the particle separation member and the vacuum cleaner further comprising a baffle positioned beneath the particle separation member at a position 10 to 20xc2x0 downstream of the position at which the air flow changes direction.
In another embodiment, the particle receiving chamber has a bottom to comprise a sealed chamber except for the apertures and the baffle extends between the particle separation member and the bottom of the particle receiving chamber.